1. Field of Invention
The present invention relates to a hydraulic height adjusting system for adjusting the height of a vehicle from the ground.
2. Description of Related Art
Hydraulic height adjusting systems for adjusting the height of the body of a vehicle from the ground known in the art generally include four hydraulic linear actuators (typically single-effect actuators), each interposed between a respective wheel and the vehicle body to change the distance between the axis of rotation of that wheel and the vehicle body, and a hydraulic circuit arranged to control the flow of a fluid (typically oil) under pressure to/from the hydraulic actuators. The maximum height of the vehicle body from the ground thus corresponds to the condition where the hydraulic actuators are fully extended, whereas the minimum height of the vehicle body from the ground corresponds to the condition where the hydraulic actuators are fully compressed or retracted. The hydraulic circuit includes a pump which provides pressurized fluid to be supplied to the hydraulic actuators, and one or more flow control valves (typically solenoid valves) for controlling the flow of the pressurized fluid to/from the hydraulic actuators. The pump and the flow control valve(s) are controlled by an electronic control unit which, taking into account data sent thereto about the speed and the height from the ground, defines and sets the desired height from the ground so as to optimize the behaviour of the vehicle suspension and/or the aerodynamic efficiency of the vehicle. Typically, at low speed, the height from the ground should be at the maximum level so as to allow the vehicle to easily clear obstacles (such as potholes or bumps) on the road surface, or to easily cross steep slopes (such as garage entry ramps) without the risk of damaging the vehicle body. At high speed, however, the height from the ground should typically be at the minimum level so as to minimize the aerodynamic drag coefficient (Cx).
With such a height adjusting system, it is possible to obtain the four main operating conditions of the vehicle: 1) a static condition of minimum height from the ground, in which all four hydraulic actuators are fully compressed; 2) a static condition of maximum height from the ground, in which all four hydraulic actuators are fully extended; 3) a dynamic condition of raising, in which the pump provides pressurized fluid which is supplied to extend the four hydraulic actuators; and 4) a dynamic condition of lowering, in which the fluid is discharged from the four hydraulic actuators which subsequently retract under the effect of the vehicle's weight.
While hydraulic height systems of the above-identified type have generally performed well for their intended purpose, there remains a need in the art for a hydraulic height system that is able to change the height of the vehicle body from the ground, even if the vehicle is running at high speed, without negatively affecting the stability of the vehicle itself.